Rigid Foam Above Roof Deck

Deck for a thick roof rigid foam insulation installed above the roof assembly can create an energy smart roof.

Rigid foam above roof deck.

The persist approach shown in that article includes rigid foam above the roof sheathing. This construction approach was first used in the 1970s and it has been implemented much more widely since it was first included in the international code council s icc model building code in 2007 irc section 806 4. Rigid foam insulation installation prepare roof deck. Of cellulose insulation in the rafter cavities the roof shown here has an r value of approximately 63.

You might be able to get away with keeping the existing roofing in place but i would recommend removing the shingles for a few reasons. More insulation is needed above the roof deck in colder climates and where indoor relative humidity is above 35 in winter. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls. Included with the article was a drawing illustrating a method using layers of polyiso with stacked 2x4 s at the eave.

The first step with roof installation is to prepare the roof deck by getting rid of all dirt dust and contaminants. High r value unvented roof assemblies will require a proportionally larger amount of insulation above the roof deck for condensation control. Foamular xps roof insulation for commercial buildings page 5 foamular xps roof insulation for commercial buildings foamular xps insulation is a rigid foam insulation which meets the needs of today s design professionals for a truly sustainable insulation product. Generally 40 of the total assembly r value should be above the roof deck.

First removing the shingles allows you to inspect the roof deck and address any questionable areas before encasing the whole thing in foam. My question was prompted by your article about using rigid foam insulation above the roof deck. The rigid insulation over roof would have controlled the temperature of the condensing surface the underside of the roof deck so that i would not have had to use the spray foam except at the perimeter to provide the air seal to the tops of the walls. The bottom layer of a single ply membrane roofing system is the roof deck or substrate.

Polyisocyanurate insulation above the sheathing and approximately 91 4 in. These 2x4s are extended at the eaves and rakes to create a roof overhang. Contributing editor michael maines. Then 2x4s usually installed on the flat are installed above the rigid foam.

The roof deck can be plywood metal concrete or wood planks. The assembly that i would like to use would be top to.